Ruthenium-CatalyzedTransfer Hydrogenation of Alkynes:Access to Alkanes and (<i>E</i>)- or (<i>Z</i>)‑Alkenes in Tandem with Pd/Cu Sonogashira Cross-Coupling

A complete reduction of alkynes using a combination of [RuCl₂(<i>p</i>-cymene)]₂, DTBM-SEGPHOS, and a paraformaldehyde/water system as the hydrogen source was developed, affording alkanes in 52–99% yields. In addition, the preparation of alkenes from terminal alkynes and aryl iodides by a tandem process of Pd/Cu-catalyzed Sonogashira reaction followed by Ru-catalyzed transfer hydrogenation is reported, affording alkenes in 38–99% yields. This multicatalysis proceeds via three consecutive reactions and can be extended further, as shown by adding an iodine-catalyzed <i>cis</i>–<i>trans</i> alkene isomerization step.